ipc: Use a global for the process's attachment broker.

content/common/gpu/gpu_channel.h

Index: content/common/gpu/gpu_channel.h
diff --git a/content/common/gpu/gpu_channel.h b/content/common/gpu/gpu_channel.h
index c51baa800265f9682f39e30c18b98c3672629ba6..fb98c889f5b60814bfd36f4a4cef6f99c4d4bbc5 100644
--- a/content/common/gpu/gpu_channel.h
+++ b/content/common/gpu/gpu_channel.h
@@ -43,7 +43,6 @@ class SubscriptionRefSet;
 }
 
 namespace IPC {
-class AttachmentBroker;
 class MessageFilter;
 }
 
@@ -75,8 +74,7 @@ class CONTENT_EXPORT GpuChannel
 
   // Initializes the IPC channel. Caller takes ownership of the client FD in
   // the returned handle and is responsible for closing it.
-  virtual IPC::ChannelHandle Init(base::WaitableEvent* shutdown_event,
-                                  IPC::AttachmentBroker* attachment_broker);
+  virtual IPC::ChannelHandle Init(base::WaitableEvent* shutdown_event);
 
   // Get the GpuChannelManager that owns this channel.
   GpuChannelManager* gpu_channel_manager() const {